Review questions for the lecture on teleosts (Jan 12, 2015)
A) What are the advantages of zebra fish for research? List at least six.
B) Please rank these advantages in order of importance, and explain your reasons. C) Are there (Is there?) any advantages that is/are absolute "deal-breaker", in the sense that no animal or plant that lacks that (those) properties could be used as model research organisms?
*D) A certain species of sponge is listed on the internet as being a "model organism", although they do not reproduce in captivity and live only on the Great Barrier Reef, along north-eastern Australia. *E) Would actual Zebras be as good as Zebra Fish as experimental animals? Why not? F) Xenopus laevis is now being replaced by Xenopus tropicalis as a "model organism" for the reason that X. laevis turned out to be tetraploid. Figure out why tetrapoidy is such a disadvantage. (Hint: genetic manipulation) G) Teleost oocytes are spherical until fertilized, but cytoplasm then flows into a hemispherical bump at the animal pole. Suggest what force would be capable of causing this flow? You are welcome to suggest two or more possible forces, or sets of forces. H) What and where is the "Yolk Syncytial Layer"? I) What and where is the "Enveloping Layer" J) What and where are the "Deep Cells" K) Which of these develop into the body of the fish? L) Draw cross-sections of teleost embryos at several stages of development? *M) If you wanted to test whether embryonic induction is a normal part of teleost development, how would you try to do this? N) How and where do teleost embryos use pinocytosis to change the surface properties of the yolk syncytial layer? O) By what ingenious method did J.P. Trinkaus greatly increase the visibility of this pinocytosis? *P) Suppose that a researcher inserted a micropipette through the enveloping layer and sucked out about half of the deep cells (before gastrulation), and then let gastrulation and body formation continue as normally as it could, which of the following might happen?
? A tail-less fish would develop, in which the head and body were normal size, but no posterior organs developed? ? Gastrulation failed to occur, and no parts of the fish developed?
? (maybe headless fish?)? What could each of these results tell us (or hint to us) about normal mechanisms of fish development? *Q) When and where would you expect each of the hox genes to begin being transcribed to make their messenger RNAs? First the most three-prime hox genes, then the hox gene next to it in the 5-prime direction, then the third one along the 3' - 5' axis? Or alternatively, would you expect all the hox genes to begin transcription at the same time? (Hint: it's the former in birds and mammals, but fish might be different.) Explain what these results could tell you about the mechanisms that control hox gene expression? *R) Design some experiments that would take advantage of one or more of the peculiarities of teleost embryos to help answer some fundamental biological question. S) Suppose that teleosts have evolved a fundamentally different set of mechanisms to neurulate, gastrulate, or to control cell differentiation (as compared with the mechanisms evolved by mammals) then does that mean that discovery of the human mechanisms will be delayed or even prevented? Argue pro or con. (Hint: in fact, teleost embryos form their neural tube by hollowing out a solid rod of cells, as compared with folding a flat sheet of epithelial cells, as occurs in all other vertebrates) T) Deep cells converge toward the body axis equally from right and left, adding themselves to the posterior end of the body (first head, then neck, then,,,, etc and finally tail. What might happen if you physically removed all or most of the deep cells to the left of the body axis, just before they had a chance to add themselves to the body? And what could each possible result tell you about normal mechanisms of development? Visualize an experiment in which deep cells from a teleost embryo were inserted into the blastocoel of a gastrulating salamander embryo. U) Compare this with Proscholdt's discovery of induction V) What alternative results could result from this graft? W) How would you interpret each possible result, in terms of what normal biological facts would have predicted each possible result, or alternatively what possible facts could be conclusively disproven? X) If conjoined twins developed from a teleost embryo, describe and sketch sequential stages by which such twinning could/would occur. *Y) Could conjoined twins develop (in any kind of animal) in such a way that very different combinations of hox genes are transcribed in one twin than the other, at the location where they are merged? Why? Why not? If this never happened, what would you interpret about the mechanism(s) that control which hox genes are expressed in different parts of the body? Z) Invent an imaginary sequence of early embryonic events, as different as possible from what actually occurs in teleosts, amphibians, birds or mammals.
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